title: Origin, evolution, and excision of internal elimination segments in germline genes of ciliates.
abstract: Three hypothesis on the evolutionary/molecular origin of internal eliminated segments (IESs) in the germline of hypotrichous ciliates are discussed in the context of the high rate of mutation accumulation in IESs, shifting of IESs during speciation, and evolutionary scrambling of segments within some hypotrich germline genes. Developmental excision of IESs from the germline in Paramecium suggests that the parental macronucleus may provide nucleic acid sequence information to guide excision of IESs and splicing of macronuclear-destined sequences. In ciliates of the oxytrichid/stylonychid group, such a mechanism could explain the precision of excision of IESs and gene unscrambling. Recently initiated molecular/genetic studies may eventually clarify the role of the parental macronucleus in IES excision and gene unscrambling as well as the molecular mechanisms of these events.
authors.affiliation: University of Colorado, Department of Molecular, Cellular and Developmental Biology 80309-0347, USA. prescotd@spot.Colorado.edu
authors.forename: D M
authors.initials: DM
authors.lastname: Prescott
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics; D016798:Ciliophora / Q000235:genetics*; D016054:DNA, Protozoan / Q000235:genetics; D019143:Evolution, Molecular; D015321:Gene Rearrangement; D017125:Genes, Protozoan; D016810:Hypotrichida / Q000235:genetics; D017384:Sequence Deletion
chemical_list: D016054:DNA, Protozoan